Inkjet printers generally have a printhead, from which the ink for printing is expelled onto a medium. The printhead (or “pen” as it is sometimes known) generally has a large number of nozzles that expel ink onto the medium with a very high degree of precision.
The printhead in a printer is generally much smaller than the medium to be printed on. The medium is therefore advanced past the printhead in a first direction (in a so-called media-feeding direction). In order to print to areas of the media perpendicular to the media-feeding direction, the printhead itself is translated across the medium in a direction perpendicular to the media-feeding direction. The width of a strip of medium that can be printed to on one translation of the printhead is called a swath, which corresponds to the height of the printhead. Therefore, substantially the whole of a two dimensional surface can be printed using one or more swaths by perpendicular advancement of the medium to each swath after completion of each swath. Thus, printing can be achieved by using a printhead, which has a maximum printhead height that is less than the dimension of the medium in the first direction. In order to ensure that the image to be printed is accurately produced, the changing positioning of the printhead relative to the medium must be highly accurate.
When regularly shaped paper is the medium pinch rollers can control the advancement of the medium accurately. However, accurate positioning of some types of media is not possible using such pinch rollers. Misalignment of the media can cause printable ink to be placed on the printer parts. Additionally, uneven loading of the pinching rollers will cause inconsistent pen to paper spacing leading to reduction of consistent drop placement on the paper and poor print quality.